What happens when sodium hydroxide is added to a solution containing Fe³⁺ ions?

When sodium hydroxide is added to a solution containing Fe³⁺ ions, a brown precipitate forms due to the formation of iron(III) hydroxide, Fe(OH)₃. This process occurs because the hydroxide ions from the sodium hydroxide react with the Fe³⁺ ions in solution.

In this reaction, the iron(III) ions hydrolyze in water, leading to the production of the insoluble hydroxide precipitate. Iron(III) hydroxide has a characteristic brown color, which is why the precipitate appears brown. This can be observed visually when the addition of sodium hydroxide causes the clear solution to turn cloudy and develop a distinct brown coloration as the precipitate forms.

Other options present scenarios that do not accurately describe the reaction with Fe³⁺ ions. The formation of a green precipitate typically relates to the behavior of iron(II) ions, not iron(III). A colorless solution would suggest that no reaction occurred, which contradicts the chemistry involved with Fe³⁺ and hydroxide ions. The evolution of a gas is also not relevant in this specific context, as the reaction primarily leads to the formation of a solid precipitate rather than a gaseous product.